Lock icon on USERPROFILE folder suddenly missing

I have a Windows 7 Pro installation with 2 accounts (administrator, standard user). When I'm logged in as administrator, there is a small lock icon on the administrators userprofile folder. When I was logged in as standard user there was a small lock icon on the standard users userprofile folder.

Since a few days the lock icon on the standard users userprofiler folder is missing when I'm logged in as a standard user. It looks like any other folder.

Why is this so, what consequences does it have (securitywise) and how can I get the lock back?